Efficacy of post-harvest rinsing and bleach disinfection of E. coli O157:H7 on spinach leaf surfaces.

Attachment and detachment kinetics of Escherichia coli O157:H7 from baby spinach leaf epicuticle layers were investigated using a parallel plate flow chamber. Mass transfer rate coefficients were used to determine the impact of water chemistry and common bleach disinfection rinses on the removal and inactivation of the pathogen. Attachment mass transfer rate coefficients generally increased with ionic strength. Detachment mass transfer rate coefficients were nearly the same in KCl and AGW rinses; however, the detachment phase lasted longer in KCl than AGW (18 ± 4 min and 4 ± 2 min, respectively), indicating that the ions present during attachment play a significant role in the cells' ability to remain attached. Specifically, increasing bleach rinse concentration by two orders of magnitude was found to increase the detachment mass transfer rate coefficient by 20 times (from 5.7 ± 0.7 × 10-11 m/s to 112.1 ± 26.8 × 10-11 m/s for 10 ppb and 1000 ppb, respectively), and up to 88 ± 4% of attached cells remained alive. The spinach leaf texture was incorporated within a COMSOL model of disinfectant concentration gradients, which revealed nearly 15% of the leaf surface is exposed to almost 1000 times lower concentration than the bulk rinse solution.

Antimicrobial behavior of novel surfaces generated by electrophoretic deposition and breakdown anodization.

Biofilms have devastating impacts on many industries such as increased fuel consumption and damage to surfaces in maritime industries. Ideal biofouling management is inhibition of initial bacterial attachment. The attachment of a model marine bacterium (Halomonas pacfica g) was investigated to evaluate the potential of these new novel surfaces to resist initial bacterial adhesion. Novel engineered surfaces were generated via breakdown anodization or electrophoretic deposition, to modify three parameters: hydrophobicity, surface chemistry, and roughness. Mass transfer rates were determined using a parallel plate flow chamber under relevant solution chemistries. The greatest deposition was observed on the superhydrophilic surface, which had micro- and nano-scale hierarchical structures composed of titanium oxide deposited on a titanium plate. Conversely, one of the hydrophobic surfaces with micro-porous films overlaid with polydimethylsiloxane appeared to be most resistant to cell attachment.

Understanding the transformation, speciation, and hazard potential of copper particles in a model septic tank system using zebrafish to monitor the effluent.

Although copper-containing nanoparticles are used in commercial products such as fungicides and bactericides, we presently do not understand the environmental impact on other organisms that may be inadvertently exposed. In this study, we used the zebrafish embryo as a screening tool to study the potential impact of two nano Cu-based materials, CuPRO and Kocide, in comparison to nanosized and micron-sized Cu and CuO particles in their pristine form (0-10 ppm) as well as following their transformation in an experimental wastewater treatment system. This was accomplished by construction of a modeled domestic septic tank system from which effluents could be retrieved at different stages following particle introduction (10 ppm). The Cu speciation in the effluent was identified as nondissolvable inorganic Cu(H2PO2)2 and nondiffusible organic Cu by X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), diffusive gradients in thin-films (DGT), and Visual MINTEQ software. While the nanoscale materials, including the commercial particles, were clearly more potent (showing 50% hatching interference above 0.5 ppm) than the micron-scale particulates with no effect on hatching up to 10 ppm, the Cu released from the particles in the septic tank underwent transformation into nonbioavailable species that failed to interfere with the function of the zebrafish embryo hatching enzyme. Moreover, we demonstrate that the addition of humic acid, as an organic carbon component, could lead to a dose-dependent decrease in Cu toxicity in our high content zebrafish embryo screening assay. Thus, the use of zebrafish embryo screening, in combination with the effluents obtained from a modeled exposure environment, enables a bioassay approach to follow the change in the speciation and hazard potential of Cu particles instead of difficult-to-perform direct particle tracking.

Synergistic effect of pH and phase in a nanocrystalline titania photocatalyst.

Titanium dioxide is a semiconducting material that has been studied for many years as a photocatalytic material to degrade organics in water. This study investigated the effect of anatase-rutile mixtures and pH on the photocatalytic degradation of the dye Methylene blue as the target analyte. Anatase-rutile mixtures between 0 and 90% rutile that were synthesized from a water-soluble precursor were suspended at pH 4, 7, and 10. Suspension pH significantly affected the reactivity and efficiency of the photocatalysts because of the particle-particle and sorbate-surface interactions. The highest removal percentage of MB by 240 min at pH 4, 7, and 10 was 35, 99, and 93%, respectively. pH 7 was ideal to observe the affect of percent rutile on the degradation rate, where 91% was removed within 120 min by the material composed of 20% rutile, which is attributed to the synergistic charge transfer of holes from rutile to anatase.